The present invention relates in general to machines for printing images on articles such as containers or packages of products.
In the description and in the appended claims, the term “image”: is intended in a broad sense to mean text, a design or logo, a bar code, or any other two-dimensional graphical representation.
It is known to print codes and/or images of other types directly onto already-packaged products by the thermal transfer of ink from an inked ribbon.
The subject of the present invention is, in particular, a type of machine for printing images comprising a support structure in which there are:    a thermal-transfer device having a movable active surface in a position operatively facing the path of the articles that are to receive the printing,    supply and guide means suitable for advancing a flexible ribbon in steps along a predetermined route which extends partly between the active surface of the thermal-transfer device and the path of the articles, the flexible ribbon carrying, at predetermined intervals, on the face which is intended to face the articles, images formed with a thermally transferable ink, and    drive means suitable for bringing about a movement of the active surface of the thermal-transfer device towards the ribbon and an article so as to press and heat the ribbon against the article in order to bring about the transfer of an image carried by the ribbon onto the article.
Typically, the movement of the thermal-transfer device towards the ribbon which carries the images and towards the article takes place vertically downwards from above.
If, during the vertical movement of the thermal-transfer device and of the portion of the ribbon which carries the image, even a slight slippage of the ribbon with the image takes place in a horizontal direction, a poor and sometimes unacceptable printing result is obtained.